Executive Summary : | Solvent responsive chitosan biopolymer thin films with engineered matrix characteristics can accomplish desirable shape-changing properties such as self-folding. The solvent can be an ionic solution, buffers, pH solutions, inorganic/organic solvent, etc. The actuation of a solvent-responsive polymer is driven by the diffusion of solvent inside the polymer matrix. The concentration gradient developed due to the diffusion of solvent across the thickness of the film creates the moment that leads to actuation. As the concentration gradient disappears, the film reverts to its initial unfolded state. These polymers provide distinctive properties such as biodegradability, biocompatibility, renewability, and inexpensiveness. Complex self-shaping patterns via solvent response have been designed to mimic the naturally occurring actuators. These patterns are made on polymer films prepared by solvent casting methods. Hydrogel or biopolymer films can be modified depending on a particular type of pattern of actuation. These modifications can be a surface coating with a hydrophobic polymer or forming a stable bilayer with other responsive polymers. The advanced technology of 4D printing enables us to fabricate dynamic structures which can change their shapes, functions, or properties along with the time when appropriate external stimuli (e.g., water, pH, temperature) are applied. A number of 3D printing techniques have been in development for the printing of hydrogels such as direct -ink writing (DIW), stereolithography (SLA), and digital light projection (DLP). Among them, DIW is a promising technique for four-dimensional(4D) printing for the development of multi-material shape-morphing structures that respond to external stimuli with high-resolution patterning, architectural freedom, and unique properties intended. Applying DIW in a 3D printing set up, we propose to design and print hydrogel based structures which can expand and collapse when exposed to solvent as external stimuli. These structures can find multiple applications in the field of biomedical devices, soft robotics etc. The details of the fabrication techniques, the approaches, the challenges involved are explained in the main proposal. |